Advertisement

Advertisement

Technology : Industrial waste can be great for the garden

By Harvey Black

A DIRTY trick is being performed in a good cause by researchers in the
US: they are turning an unpromising group of waste products into a pseudo-soil
that can improve the quality of inferior earth and help to reclaim land damaged
by industry.

The mixture contains equal amounts by weight of coal ash and leftover
biosolids—nutrients and dead bacteria used in a fermentation process by
Eli Lilly to make antibiotics, says Joseph Mikesell, director of utilities at
Purdue University in Indiana, where the research is being carried out. The final
ingredients are half as much again of garden waste, and wood chips which are
mixed in to allow air to circulate through the mixture, says Mikesell.

Once mixed, the artificial soil is left to sit for up to six months in a
compost heap. During that time, oxygen and moisture content are monitored and
regulated to ensure that conditions are right for the bacteria in the garden
waste to digest the organic material.

The ash from the coal provides important soil nutrients, including nitrogen,
sulphur and calcium, says Jody Tishmack, ash management coordinator at Purdue,
who is helping guide the project. The ash is produced in the university’s power
stations using fluidised bed combustion, where coal is burnt with limestone. The
limestone absorbs the sulphur in the coal and reduces toxic emissions. The ash
meets limits for heavy metals set by the US’s Environmental Protection
Agency.

Advertisement

Tests in greenhouses show that when the mixture is blended with poor-quality
soil such as clay, sand or gravel, which has little organic matter, it can
easily grow healthy stands of crops such as wheat and alfalfa.

Six hundred tonnes of the “manufactured soil” have been spread on 1.5
hectares of land damaged by acid drainage from the Chinook Mines in Brazil,
Indiana. A layer of pseudo-soil 4 centimetres thick has been spread on three
half-hectare test plots. The researchers hope the land will eventually support
grass and other vegetation that will reduce the acidity. Currently the
acid-damaged land will not support vegetation.

The soil will also be used in a project to reclaim gravel pits covering an
area of 220 hectares near the university, says Tishmack. The soil could also be
mixed with sand and gravel and used for landscaping at new construction sites.
This would be much cheaper than adding new topsoil, she says.

While the results of the greenhouse experiments are promising, the
researchers say the true test of the Purdue soil will only come now it is being
tried in the outside world.

Tishmack says it is doubtful that the soil will be used on farms as it would
cost about &dollar;5000 per hectare to spread a 30-centimetre layer.